This was what I expected.
After I ran into trouble I figured out that by default
the PCI-BUS arbiter is turned off.
To do realtime transfer we turned on the arbiter inside
the PCI-CHIP-SET.
Now the arbiter stops long term transfers to reschedule the
PCI master ownerchip. Works fine for me :)
Jens Michaelsen
Kulwinder Atwal schrieb:
> Philip N Daly wrote:
> >
> > Hi all,
> >
> > Not specifically real time Linux but does anyone know:
> >
> .
> .
> .
> > 2. How long the delay is when reading from a PCI card ... i.e. if
> > the operation value = readPCI(channel) is atomic, how long would
> > it take to execute that instruction (again in ns, us, ms)?
>
> Typical 33 MHz PCI hardware latencies are 10-20 uSec according to an IBM
> datasheet. Add to this any delays caused by the 'readPCI' code running
> on the CPU before and after the read. The PCI 2.1 Specification has two
> equations for calculating bus latencies after a device wins arbitration
> of the bus:
>
> worst case:
>
> latency (bus clocks) = 16 + 8*(n-1)
>
> n = number of 32 bit words transferred
> bus clocks = 1/33 MHz or 1/66 MHz depending on your PCI bus speed.
>
> typical case:
>
> latency (bus clocks) = 8 + 8*(n-1)
>
> The arbitration latency is:
>
> m * Latency Timer
>
> m = number of masters ( max is 8 )
> Latency Timer = typical is 22 bus clocks
>
> Your total PCI bus delay is the sum of the two latencies.
>
> - Each device can have a different timer setting. Check the settings
> of your devices.
> - Some devices can do an endless data transfer without a timer.
> - Normal Linux can start a PCI data transfer that can run into
> a real time Linux interval.
>
> Experiment with your system setup. If you need shorter delays stop any
> unnecessary Linux PCI transfers. Plan the transfers better.
>
> The PCI 2.1 Specification is available for download at:
>
> http://akulin.npi.msu.su/docs/standard/pci21.pdf
>
> Latencies are covered in section 3.5.
>
> - Kal.
>
> >
> > Thanks in advance,
> >
> > +==================================================================+
> > Phil Daly, NOAO/AURA, 950 N. Cherry Avenue, Tucson AZ 85719, U S A
> > E-mail: [EMAIL PROTECTED] V-mail: (520) 318 8438 Fax: (520) 318 8360
> >
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